The present invention relates generally to rear view mirrors for vehicles and more particularly to an improved rear view mirror assembly (1) which eliminates the blind spot that normally occurs just before the passing vehicle comes abreast of the lead vehicle (2) which more accurately reflects the position and movement of the passing vehicle as the latter approaches the lead vehicle, and (3) which in one embodiment provides a field of view that not only eliminates the blind spot but also incorporates the rear tires on the mirror supporting side of the lead vehicle.
In the past, it has been general practice by most drivers, especially drivers of tractor-trailers and recreational vehicles to use two rear view mirrors on one side of the vehicle, a main mirror and a secondary mirror. Typically, this main mirror is large and planar for providing a view back down the road a substantial distance behind the driver, especially since its usual field of view is limited to about 10.degree.. On the other hand, the secondary mirror is typically smaller and consists of a convex section of a sphere, generally referred to as a "bulls eye" mirror. This latter mirror is utilized to eliminate the blind spot located to one side of the driver of the lead vehicle and its use is limited to that general field of view. As a result, the driver is required to move his eyes from one mirror to the other in order to keep track of the other vehicles on the road. Moreover, because the "bulls eye" mirror is spherical in nature and typically defines a relatively small radius of curvature the image reflected is badly distorted both in its vertical and horizontal planes.
The general effect of the "bulls eye" mirror is to give a distorted view of the size and speed of the oncoming vehicle. More specifically, as this latter vehicle approaches the blind spot of the main mirror, the image in the secondary "bulls eye" mirror is quite small (in all dimensions) relative to the actual size of the vehicle. However, as the oncoming vehicle moves forward and comes nearly abreast of the driver, the image appears to grow in size and "jump out" from the mirror at such a rapid rate as to exaggerate its forward speed. The problem is that the image is at first so small as to make the approaching vehicle appear to be at a considerable distance behind the driver's vehicle until the "jumping out" effect which occurs only when the approaching vehicle is already at an unsafe nearness. Because of this "jumping out" effect and movement of the eyes from one mirror to the other, safety to the drivers of the lead vehicle and passing vehicle as well as others in the near vicinity are threatened by the inability of the driver of the lead vehicle to quickly and accurately judge the situation as it relates to the passing vehicle. Because of these difficulties many drivers choose to ascertain the presence of a passing vehicle by turning their heads for a fraction of a second just before starting to pass another vehicle themselves. This, of course, causes a momentary distraction of the driver's view ahead where new hazards may suddenly occur.
There have been some suggestions in the prior art for eliminating some of the problems discussed above. For example, German Pat. No. 1,921,076, dated Nov. 19, 1970 discloses a rear view mirror including an overall mirrored surface having a planar section and an integral curved section which together presumably provide the same field of view as the planar mirror and separate convex mirror discussed above. While this patent appears to eliminate the problems associated with using two distinct mirrored assemblies for eliminating the blind spot and for viewing substantial distances rearwardly, it does not address itself to the problem of distortion (of speed and size) discussed previously. Specifically, this reference does not teach or suggest any means or method for eliminating the exaggerated way in which the on-coming or trailing vehicle is viewed as the latter approaches the lead vehicle.
Another prior art reference which combines two mirrored surfaces for increasing the field of vision is U.S. Pat. No. 4,012,125 (Hart), dated Mar. 15, 1977. However, like the German patent, this reference does not address itself to the problem of image distortion with respect to size and speed (jumping out effect) as the passing vehicle approaches the lead vehicle. In fact, this patent specifically teaches the utilization of mirrored surfaces each having a constant magnification (which includes demagnification) ratio M, at least in horizontal planes through the mirrored surfaces. One object of the patent was to eliminate angular distortion and this was achieved by maintaining a constant magnification ratio. However, Applicant has found that as the image of an approaching vehicle moves horizontally across the mirrored surface of the lead vehicle it does so at a speed which, by virtue of the constant magnification ratio of the mirrored surface, seems grossly distorted relative to the speed of the oncoming vehicle. In this regard, Applicant has found that a linear relationship between movement of the trailing vehicle and its image across the mirror eliminates such distortion. However, since each of the mirrored surfaces disclosed in the Hart patent is designed with a constant magnification ratio in the horizontal plane, Applicant has also found that there cannot be a linear relationship between the position of the passing vehicle and the horizontal position of its image on the mirrored surface, as viewed from a given observation point, specifically the eyes of the driver of the lead car. This does not mean however, that any mirrored surface having a magnification ratio which varies across its horizontal extent automatically defines the linear relationship just discussed. As will be seen hereinafter, the mirrored surface must be of a particular curvilinear configuration to provide this type of linear relationship as will be described hereinafter. Applicant has discovered that distortion of the type described can thus be reduced by providing a curved surface based on a changing magnification ratio (to be described hereinafter). The rear view mirror assembly constructed in accordance with the present invention includes such a mirrored surface, thereby reducing and preferably eliminating the distortion described above, as will also be seen.
In addition, the assembly of the present invention eliminates the aforedescribed blind spot and, in a particular embodiment, it provides a relatively wide field of view including the rear tires of the mirror-mounted side of the vehicle as well as a tailgating vehicle. This wide field of view is attained even for mirrors mounted relatively high on large trailer trucks and the like by providing a vertical curvature similar to the horizontal curvature described above, as will be seen.